This invention concerns an improved process for preparing vicinal glycol ester compounds, including ester derviatives of ethylene glycol, by reaction of oxides of carbon with hydrogen.
In copending, commonly assigned application Ser. No. 103,765, filed Dec. 14, 1979, the inventive process concerns the synthesis of glycol esters, particularly the ester derivative of ethylene glycol, by the catalytic reaction of carbon monoxide and hydrogen in the presence of a liquid medium containing a carboxylic acid co-reactant such as acetic acid. Catalysis is effected in the presence of a catalyst containing osmium or ruthenium transition metals, with the latter being most preferred. The process is exemplified by, but not limited to, the one step synthesis of ethylene glycol diacetate, from carbon monoxide, hydrogen mixtures -- commonly known as synthesis gas -- in the presence of an acetic acid (HOAc) liquid medium according to the stoichiometry of eq I below: ##STR1## Other valuable products include methyl acetate and ethyl acetate as follows: EQU 2CO+4H.sub.2 +HOAc.fwdarw.CH.sub.3 CH.sub.2 OAc+2H.sub.2 O (2) EQU CO+2H.sub.2 +HOAc.fwdarw.CH.sub.3 OAc+H.sub.2 O (3)
Methyl and ethyl acetates are used widely as solvents, primarily for surface coatings.
While use of synthesis gas is known as a building block in making a variety of chemicals there is no simple, direct, yet economical route toward production of glycol ester using relatively inexpensive catalysts. Catalysts used in making the glycol esters or free glycol material directly have proven to be very costly and/or in short supply. Glycol esters such as glycol acetate may be easily hydrolyzed to the free glycol as set out in Belgium Pat. No. 749,685 and other publications. Ethylene glycol is a particularly important component in making polyester fiber and in formulating antifreeze compositions.
Thus, in recent years, a large number of patents have been isused dealing with the synthesis of lower molcular weight hydrocarbons, olefins, alkanols etc. from synthesis gas. Of particular note U.S. Pat. No. 2,636,046, discloses the synthesis of polydydric alcohols and their derivatives by reaction between carbon monoxide and hydrogen at elevated pressures (&gt;1500 atm or 22,000 psi) and temperatures to 400.degree. C. using certain cobalt-containing catalysts. More recently, in Belguim Pat. No. 793,086 and U.S. Pat. No. 3,940,432 there is described the cosynthesis of methanol and ethylene glycol from mixtures of carbon monoxide and hydrogen using a rhodium complex catalyst. Typically, CO-hydrogenation is effected at 8000 psi of 1:1 H.sub.2 /CO synthesis gas, at 220.degree. C., using tetraglyme as the solvent, and dicarbonylacetylacetonatorhodium(I) in combination with an organic Lewis base as the catalyst precursor. (For summary of the work, see: R. L. Pruett, Annals New York Academy of Sciences, Vol. 295 p. 239 (1977)). While other metals of Group VIII of the Periodic Table have been tested for activity under similar conditions, including cobalt, ruthenium, copper, manganese, iridium and platinum, only cobalt was found to have slight activity. The use of ruthenium compounds in particular failed to produce polyfunctional products such as ethylene glycol. This is illustrated in U.S. Pat. No. 3,833,634 for solutions of trirutheium dodecacarbonyl.